Magnetic preferential orientation of metal oxide superconducting materials

Abstract

A superconductor comprised of a polycrystalline metal oxide such as YBa 2 Cu 3 O 7-X (where 0<X<0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. The highly anisotropic diamagnetic susceptibility of the polycrystalline metal oxide material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A method of forming a superconducting metal oxide with improved current carrying capacity wherein said superconducting metal oxide has a polycrystalline structure and is anisotropically superconducting having one or more longer crystal axes along which said metal oxide is superconducting, said method comprising the steps of: reducing the superconducting metal oxide to a flakelike, powder form, wherein the metal oxide powder is comprised of particles of single crystals, said superconducting metal oxide having a characteristic critical temperature below which it is superconducting;   mixing said metal oxide single crystal particles with binder and solvent to form a slip;   lowering the temperature of said metal oxide single crystal particles in said slip to said characteristic critical temperature;   directing a magnetic field onto said slip to orient said metal oxide single crystal particles along a preferential direction such that said one or more longer axes of each of said metal oxide crystals are in general alignment; and   removing the binder and solvent from the oriented metal oxide single crystal particles and sintering said metal oxide single crystal particles.   
     
     
       2. The method of claim 1 further comprising the step of mixing said metal oxide single crystal particles with a liquid comprised of a solvent and a dispersing agent. 
     
     
       3. The method of claim 2 wherein said solvent is an alcohol. 
     
     
       4. The method of claim 3 wherein said dispersing agent is a phosphate ester. 
     
     
       5. The method of claim 1 further comprising the step of heating the mixture of said metal oxide single crystal particles and said liquid after said metal oxide single crystal particles are aligned to remove the liquid therefrom. 
     
     
       6. The method of claim 1 further comprising the step of allowing the liquid to evaporate from the mixture of said metal oxide single crystal particles and said liquid after said metal oxide single crystal particles are aligned along said preferential direction. 
     
     
       7. The method of claim 1 further comprising the step of mechanically working the metal oxide single crystal particle and liquid mixture after said metal oxide single crystal particles are aligned along said preferential direction to effect further alignment of said metal oxide single crystal particles. 
     
     
       8. The method of claim 7 wherein the step of mechanically working the metal oxide crystal powder and liquid mixture includes tape casting the mixture. 
     
     
       9. The method of claim 7 wherein the step of mechanically working the metal oxide crystal powder and liquid mixture includes slip casting the mixture. 
     
     
       10. The method of claim 7 wherein the step of mechanically working the metal oxide crystal powder and liquid mixture includes extruding the mixture. 
     
     
       11. The method of claim 1 wherein said superconducting metal oxide has a characteristic critical temperature below which it is superconducting, said method further comprising the step of using the room temperature paramagnetism of the said superconducting material so as to align in a slip at room temperature. 
     
     
       12. The method of claim 11 wherein said superconducting metal oxide is yttrium barium copper oxide said wherein the step of converting said superconducting metal oxide to a paramagnetic material includes substantially replacing yttrium atoms in said yttrium barium copper oxide with rare earth atoms. 
     
     
       13. The method of claim 12 wherein said rare earth atoms are dysprosium. 
     
     
       14. The method of claim 12 wherein said rare earth atoms are holmium. 
     
     
       15. The method of claim 12 wherein said rare earth atoms are erbium.